Abstract
The mechanism of slow muscarinic excitation in bullforg sympathetic ganglia was studied using a singleelectrode voltage clamp technique. The membrane current induced by muscarine (0.01–30 μM:I mus) consisted of a voltage-dependent component (dI M) induced by the inhibition of K+-current (known asI M), a voltage-independent cation-selective current (I D), or both. In the last case, the magnitude of either component varied in different cells. Generation of bothdI M andI D were equally suppressed by pirenzepine with a dissociation constant (K i) of 30 nM, while they were inhibited less by AF-DX116 with aK i of 600 nM.K d values for muscarinic induction ofdI M andI D were 0.35 and 5 μM respectively. This difference was also seen even after reducing the receptor population by pretreatment with propylbenzilylcholine mustard.I D was enhanced after blockade ofdI M by Ba2+ (4 mM), with a little change inK d. This effect was larger when the controlI D was smaller. These results suggest that a single subtype (M1) of muscarinic receptor generates both thedI M andI D with different efficacies and that Ba2+, known as a blocker ofI M (accordingly of a high-efficacy current,dI M), potentiates a low-efficacy current (I D).
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Tsuji, S., Kuba, K. Muscarinic regulation of two ionic currents in the bullfrog sympathetic neurone. Pflugers Arch. 411, 361–370 (1988). https://doi.org/10.1007/BF00587714
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DOI: https://doi.org/10.1007/BF00587714